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Crystal, Magnetic, and Electronic Structures, and Properties OPEN Crystal, magnetic, and electronic SUBJECT AREAS: structures, and properties of new MAGNETIC PROPERTIES AND MATERIALS BaMnPnF(Pn 5 As, Sb, Bi) SUPERCONDUCTING PROPERTIES AND MATERIALS Bayrammurad Saparov1, David J. Singh1, Vasile O. Garlea2 & Athena S. Sefat1 SOLID-STATE CHEMISTRY ELECTRONIC PROPERTIES AND 1Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA, 2Quantum Condensed MATERIALS Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. Received New BaMnPnF(Pn 5 As, Sb, Bi) are synthesized by stoichiometric reaction of elements with BaF2. They 26 March 2013 crystallize in the P4/nmm space group, with the ZrCuSiAs-type structure, as indicated by X-ray crystallography. Electrical resistivity results indicate that Pn 5 As, Sb, and Bi are semiconductors with band Accepted gaps of 0.73 eV, 0.48 eV and 0.003 eV (extrinsic value), respectively. Powder neutron diffraction reveals a 20 June 2013 G-type antiferromagnetic order below TN 5 338(1) K for Pn 5 As, and below TN 5 272(1) K for Pn 5 Sb. Magnetic susceptibility increases with temperature above 100 K for all the materials. Density functional Published calculations find semiconducting antiferromagnetic compounds with strong in-plane and weaker 8 July 2013 out-of-plane exchange coupling that may result in non-Curie Weiss behavior above TN. The ordered magnetic moments are 3.65(5) mB/Mn for Pn 5 As, and 3.66(3) mB/Mn for Pn 5 Sb at 4 K, as refined from neutron diffraction experiments. Correspondence and requests for materials he recent discovery of high temperature superconductivity in F-doped LaFeAsO1 (1111 family) initiated an should be addressed to extensive research into analogous materials. This research led to the discoveries of superconductivity in B.S. (saparovbi@ornl. 2,3 4 5 T doped BaFe2As2 (122 family), LiFeAs (111 family), and FeSe (11 family), among others. All these families gov) feature two dimensional (2D) structures with FeAs or FeSe layers, which contain edge-shared FeAs4 or FeSe4 tetrahedra. Fe atoms are formally divalent; hole-, electron-, or isovalent-doping inside or outside of layers can result in superconductivity. Among the Fe-based superconductors (FeSCs), the highest superconducting transition temperatures (TCs) are reported for the 1111 family6,7. In the search for non-Fe-based oxypnictides, varieties of physical properties are found such as diamagnetism in LaZnAsO8, itinerant ferromagnetism in LaCoAsO9,10, semiconducting antiferro- 11 12 magnetism in LnMnPnO (Ln 5 La-Sm; Pn 5 P, As) and superconductivity in LaNiAsO (TC , 3 K). Interestingly, although such oxyarsenides have been studied in detail, reports on non-oxide 1111 fluoroarsenides with ZrCuSiAs-type structure, i.e. BFeAsF (B 5 alkaline-earth metal), are relatively scarce. For the 1111 fluopnictides BFeAsF, rare-earth substitution at the alkaline-earth metal (B) site is found to give the 13,14 highest TC of 56 K for Sr0.5Sm0.5FeAsF and Ca0.4Nd0.6FeAsF . The only known non-Fe transition-metal-based 1111 fluoropnictides are BaMnPF15, ACuChFandAAgChF(A 5 Sr, Ba, Eu; Ch 5 S, Se, Te)16,17.However,itshould be noted that Cu and Ag in ACuChFandAAgChF are nominally monovalent, and therefore, BaMnPF is the only known 1111 fluoropnictide containing divalent non-Fe transition metal. Other known 1111 fluoropnictides, include those of group 12 metals, namely SrZnPF, BaZnPF, BaZnSbF and BaCdSbF15,18. According to literature on the properties of 1111 fluoropnictides, SrCuChF19,20,BaCuChF21 and EuCuChF20 (Ch 5 S, Se and Te) are p-type semiconductors with Seebeck coefficients ranging from 110 to 1620 mV/K. BaZnPF15 and BaCdSbF18 are also semiconductors with band gaps of Eg 5 0.5 eV and 0.25 eV, respectively. Moreover, BaMnPF is a semiconducting antiferromagnet with a temperature independent magnetic susceptibility up to 300 K15. Considering the fact that doped BFeAsF fluoropnictides are among the highest TC (56 K) FeSCs, there is an incentive to explore for superconductivity in similar 1111 structures, and even non-Fe-based analogs. This is the report of the synthesis of new 1111 ZrCuSiAs-type BaMnPnF(Pn 5 As, Sb, Bi) (Figure 1) and a comprehensive study of their crystal, magnetic, and electronic structures. We report nuclear structures from powder and single crystal X-ray diffraction, and magnetic structures from neutron powder diffraction. In addition, we present thermodynamic and transport properties from temperature dependent electrical transport data, temperature- and field-dependent magnetization data. Moreover, we report density functional theory (DFT) electronic struc- ture calculations. SCIENTIFIC REPORTS | 3 : 2154 | DOI: 10.1038/srep02154 1 www.nature.com/scientificreports Table 2 | For BaMnPnF(Pn 5 Sb, Bi), atomic coordinates and a equivalent isotropic (Ueq ) displacement parameters, at 173 K, from single crystal X-ray diffraction refinements ˚ 2 Atom Wyckoff site xy zUeq (A ) BaMnSbF Ba 2c 0.25 0.25 0.3539(1) 0.0113(3) Mn 2a 0.25 0.75 0 0.0117(4) Sb 2c 0.25 0.25 0.8321(1) 0.0108(3) F2b 0.25 0.75 0.5 0.013(1) BaMnBiF Ba 2c 0.25 0.25 0.3585(2) 0.0205(5) Mn 2a 0.25 0.75 0 0.0210(8) Bi 2c 0.25 0.25 0.8245(1) 0.0205(4) F2b 0.25 0.75 0.5 0.023(3) Figure 1 | Tetragonal ZrCuSiAs-type structure of BaMnPnF(Pn 5 As, a Ueq is defined as one third of the trace of the orthogonalized Uij tensor. Sb, Bi). The unit cell contains transition metal pnictide layers of 2 [MnPn] that are made of MnPn4 tetrahedra. distances shown by the distance between barium and pnictogen Results atoms in adjacent layers are dBa-Sb 5 3.6489(6) A˚ in BaMnSbF and ˚ Synthesis, crystal chemistry, and stability. Three new compounds dBa-Bi 5 3.671(1) A in BaMnBiF. For comparison, MnAs4 tetrahedra of BaMnAsF, BaMnSbF and BaMnBiF are synthesized using the in BaMnAsF are characterized by the distances dMn-As 5 2.60460(4) ˚ ˚ solid-state sintering method. The compounds crystallize in the A and dMn-Mn 5 3.0221(1) A, and bond angles 109.0789(8)u and primitive ZrCuSiAs-type tetragonal P4/nmm (No. 139, Pearson 110.259(2)u, from the room temperature PXRD data (see Table symbol tP8), and are isotypic to the lighter BaMnPF (Figure 1)15. S1). The bond distances and angles in BaMnPnF are very close to 24–26 EDS results confirm the presence of small crystallites with those reported for the related BaMn2Pn2 ternary phases , which 2 2 BaMnSbF and BaMnBiF compositions after the first heating step, also contain anionic ? [MnPn] layers. which allows for collection of single-crystal x-ray diffraction data PXRD patterns along with Rietveld refinements results for (Table 1). There are four crystallographically unique atoms in the BaMnAsF, BaMnSbF and BaMnBiF are illustrated in Figures 2 to 4. asymmetric unit cell, all located in special positions (Tables 2, 4, S1). There are no Bragg peaks in the 2h range of 5–20u for Pn 5 As and BaMnPnF structure, similar to LaFeAsO, can be viewed with cationic Sb, and so the low angle regions are not shown for them. The broad 2 1 2 2 ?[BaF] and anionic ? [MnPn] layers alternating along the c-axis. background below 2h , 25u in Pn 5 Sb and Bi (Figure 3–4) are These layers are built upon edge-sharing FBa4 and MnPn4 tet- caused by the polycarbonate cover. X-ray diffraction refinement rahedra, respectively. Following the discovery of superconductivity detects a small amount of BaF2 crystalline impurity (less than 1% in the F-doped LaFeAsO, the ZrCuSiAs-type structure and its rela- by mass) in Pn 5 As and Bi products, whereas no impurity peaks are tionship with other structures have been extensively studied11,22,23. observed in the Pn 5 Sb compound. From single crystal X-ray data (Table 3), Mn-Sb and Mn-Bi bond All BaMnPnF samples have MnO impurities if ground in air dur- 2 ˚ distances in the [MnPn] layers are dMn-Sb 5 2.7767(5) A and dMn-Bi ing sample sintering stages. Even in the final product form, ground- ˚ 5 2.8479(11) A, respectively; the Mn-Mn distances are dMn-Mn 5 in-air BaMnSbF shows signs of oxidation in the PXRD data, while ˚ ˚ 3.1595(4) A in BaMnSbF and dMn-Mn 5 3.196(1) A in BaMnBiF. The BaMnBiF burns in air. The extreme air sensitivity of ground tetrahedral angles are 110.65(1)u and 107.14(3)u in MnSb4, and BaMnBiF limits its full characterization through neutron diffraction 111.73(3)u and 105.04(5)u in MnBi4 tetrahedra. The interlayer experiments. Notwithstanding these facts, the heating of pellets under ambient conditions up to 130uC and subsequent PXRD mea- surements demonstrate that BaMnPnF are air-stable in pellet form. 5 Table 1 | For BaMnPnF(Pn Sb, Bi), selected single crystal X-ray The refined room temperature lattice parameters from the PXRD diffraction data and structure refinement parameters data are a 5 4.2739(1) A˚ and c 5 9.5875(2) A˚ for BaMnAsF (Rp 5 Empirical formula BaMnSbF BaMnBiF 8.54%, wRp 5 11.52%), a 5 4.4791(1) A˚ and c 5 9.8297(2) A˚ for BaMnSbF (Rp 5 4.59%, wRp 5 6.03%), and a 5 4.5384(1) A˚ and c 5 Temperature, K 173(2) 9.8929(2) A˚ for BaMnBiF (Rp 5 4.05%, wRp 5 5.40%). The refine- Radiation, A˚ Mo Ka, 0.71073 Crystal system Tetragonal ment of PXRD data on BaMnAsF and BaMnSbF show (Figures 2b, Space group, ZP4/nmm (No.
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